Autoradiography is being used to study the birth dates (terminal mitoses and migration patterns of different populations of neurons in the spinal cord of chick embryos. Deafferentation of the embryonic hindlimb of the check embryo by early embryonic neural crest removal is being used to study the role of sensory input in limb motility and the formation of neuronal circuits for locomotion in the spinal cord. Tracer studies using HRP are being performed to identify the location of motor neuron pools which supply specific muscles in normal and transplanted limbs in the chick embryo. BIBLIOGRAPHICH REFERENCES: V. Hamburger. 1975. Cell death in the development of the lateral motor column of the check embryo. J. Comp. Neurol. 160: 535-546. V. Hamburger. 1975. Changing concepts in developmental neurobiology. Prospectives in Biology and Medicine 18: 162-178.